NSF PR 01-48 - May 31, 2001
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Marine Snail Study Suggests Conservation Efforts
Should Move Beyond Genetic Diversity
A study of climate-induced evolutionary change in
a California intertidal snail suggests that conservation
plans for protecting endangered or threatened species
should not focus exclusively on genetic diversity.
The research is funded by the National Science Foundation
(NSF).
In the study, detailed in the June 1 issue of Science,
biologists at the University of California, San Diego,
and Louisiana State University measured the genetic
diversity of populations of Acanthinucella spirata,
a common marine gastropod from San Francisco to San
Diego. They discovered that the snail's genetic diversity,
the most commonly used gauge of a population's health,
is highest in the Los Angeles area and lowest in the
northern part of its range.
"This novel study provides a new angle to research
on genetic/morphologic diversity," says Rich Lane,
director of NSF's geology and paleontology program,
which funded the research. "It has been thought that
morphologic variation is greatest in populations where
genetic diversity is highest. While that may be logical,
here is a case where it is not true. The bottom line
is that greater care and investigation may be needed
in choosing locations of biological reserves, and
in considering environmental and ecological decisions."
Measurements of genetic diversity now greatly influence
decisions on where to locate protected reserves, since
the most genetically diverse populations are assumed
to be better able to withstand environmental changes.
But while the snails around Los Angeles and southward
are genetically more diverse than those to the north,
the researchers discovered that they are less diverse
morphologically. This is due to the presence of a
different shell form, or morphology, in some populations
in the northern part of the range that is not found
in the Los Angeles area or in regions to the south.
"There's a big difference in the morphology-in the
shape and size of the shells-between the northern
and the southern populations," says Kaustuv Roy, a
biologist at UCSD who conducted the study with Michael
E. Hellberg, a biologist at LSU, and Deborah P. Balch,
a former student at UCSD. "Looking at the coast today,
there's a dramatic decline in genetic diversity in
this species going from south to north," he adds.
"But the northern regions have a greater amount of
morphological diversity. So, which do you use to make
conservation decisions-genetic diversity or morphological
diversity? Here's a case where the two come into conflict."
During many previous ice ages, the cooling of the
planet caused localized extinctions of many populations
of marine and terrestrial organisms near the northern
limits of their ranges. When the earth warmed, some
of the southern populations re-colonized the previously
occupied northern regions. This is what the scientists
believe happened to Acanthinucella spirata,
because the snail's genetic diversity is highest around
Los Angeles and declines sharply northward. The decline
in genetic diversity suggests that the northern part
of the range of this marine snail was re-colonized
by a small number of individuals from the south, resulting
in genetically homogeneous populations to the north.
The researchers obtained their estimates on when this
new morphological type arose by calculating the changes
over time in a protein they used as a "molecular clock."
They also confirmed from their fossil collections
that this second distinct morphology was not present
along the California coast before this time period.
Photographs of the two forms of Acanthinucella spirata
available at: http://ucsdnews.ucsd.edu/newsrel/science/mcshell.htm
Credit: Kaustuv Roy, UCSD
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